The present invention generally relates to new tetrafluoroethylene products with enhanced crystallinity and processes for producing the same.
For purposes of this patent, the following terms are defined. As used herein, the term xe2x80x9csinteredxe2x80x9d means and refers to being subjected to compression. As used herein, the term xe2x80x9clubricantxe2x80x9d or xe2x80x9clubricantsxe2x80x9d means and refers to a substance or substances that reduces(s) friction between moving parts and/or provide(s) cooling for moving parts. The characteristics of a lubricant are well known in the art and are fully incorporated herein. As used herein, the term xe2x80x9cunsinteredxe2x80x9d means and refers to not being subjected to pressure. As used herein, the term xe2x80x9cTFExe2x80x9d means and refers to tetrafluoroethylene (the chemical formula is C2F4,). As used herein, the term xe2x80x9cPTFExe2x80x9d means and refers to polytetrafluoroethylene (the chemical formula is (C2F4)n where n is any number). As used herein, the term xe2x80x9cpartially degraded TFExe2x80x9d means and refers to commercially available degraded TFE.
Certain terms used in the lubrication art and/or lubricant art have identified meanings. As used herein, the term xe2x80x9cburnishxe2x80x9d or xe2x80x9cburnishedxe2x80x9d or xe2x80x9cburnishingxe2x80x9d means and refers to polishing and/or wiping of a lubricant to a surface or asperities. As used herein, the term xe2x80x9casperitiesxe2x80x9d means and refers to tiny imperfections, ridges or projections on wear surfaces. As used herein, the term xe2x80x9cwear surfacexe2x80x9d or xe2x80x9cwear surfacesxe2x80x9d means and refers to an area of at least two surfaces in contact or close to contact. As used herein, the term xe2x80x9cboundaryxe2x80x9d means and refers to an area of contact between surfaces. As used herein, the term xe2x80x9cboundary periodxe2x80x9d means and refers to a period of time where surfaces are in contact without a lubricant. As used herein, the term xe2x80x9cboundary lubricationxe2x80x9d means and refers to a character of lubrication between surfaces. Heat of fusion means and refers to an increase in internal energy that is required to convert a solid to a liquid. Conversely, a reduction in internal energy can cause liquids to freeze or solidify. The heat of fusion of a substance is the heat exchange required to melt one gram of the substance (calories/gm).
Tetrafluoroethylene is well known and used for a variety of purposes. One of the greatest uses for tetrafluoroethylene is as a solid lubricant. As a lubricant, tetrafluoroethylene performs well as compared to natural lubricants and synthetic lubricants. Both natural and synthetic lubricants may be found either as liquids, semi-liquids, solids, and/or amorphous solids. Generally, examples of natural lubricants include such items as, but are not limited to, organic oils, mineral oils, grease and graphite.
Many lubricants are designed to burnish wear surfaces to improve the boundary lubrication and reduce the boundary period. Other lubricants have been developed to protect a surface from abrasion, water damage, and the like by burnishing a lubricant on the surface. Further, other lubricants have been developed as nucleating fillers for a variety of thermoplastics.
As stated, one of the most popular and widely used lubricants is PTFE (or polymerized tetrafluoroethylene), which is the subject of U.S. Pat. No. 2,230,654. The product became known as TEFLON. This product has been noted as having superior lubricating properties, primarily because of its low coefficient of friction. Many uses have.developed for this product, including, but not limited to, utilizing the material as a solid or as a dispersed solid in a carrier. As well, this product has been shown to be resistant to a wide variety of chemical attacks and thus very resilient once applied.
Other notable and desirable properties of TEFLON are:
1) TEFLON is Non-polar. The carbon backbone of PTFE is completely covered by the xe2x80x9celectron cloudxe2x80x9d of Fluorine atoms. This covering, and the angles at which the Carbon-Fluorine bonds are disposed, causes the center of electronegativity and electropositivity to be perfectly balanced through the polymer cross section. As a result no net charge difference prevails.
2) The Bond Strength of TEFLON is high. Carbon-Fluorine and Carbon-Carbon bonds are among the strongest in single bond organic chemistry.
3) TEFLON has a high degree of polymerization. The chains are most commonly very long and substantially unbranched. The low interpolymer chain attraction requires very long chain lengths in order to tangle and form together.
4) TEFLON has high thermal stability. The strength of the Carbon-Fluorine bond and the Carbon-Carbon bond translates into a relatively high heat of fusion.
5) TEFLON is relatively insoluble in normal conditions.
6) TEFLON demonstrates superb inertness to chemical and biological attack. The bonds do not react with most chemicals, Alkali metals being a notable exception.
7) TEFLON is flame resistant. TEFLON will burn, but only when in direct flame.
8) TEFLON is inert. So long as the TEFLON is not being incinerated, it can be disposed of with industrial and domestic waste. TEFLON is only harmful when heated above 400 degrees Celsius where it gives off tetrafluoroethylene, hexafluoroethylene, hexapropylene, and other fluoro compounds and toxic fumes.
9) TEFLON has low water absorbtivity. TEFLON predominantly only absorbs water after the TEFLON has been in the water long enough for the water to become physico-chemically associated with the polymer chains.
While there are several formulations of TEFLON, the most common form is PTFE. Other forms include FEP and PFA. The following chart gives generally accepted values for various properties of these three forms of TEFLON.
The ""654 patent states that polymeric tetrafluoroethylene white powders, brown powders, and/or jellies that are insoluble in hot or cold water, acetone, ether, petroleum ether, ethyl alcohol, iso-amyl alcohol, carbon tetrachloride, dichlorobenzene, ethyl acetate, pyridine, nitrobenzene, 30% NaOH, petroleum oil, glacial acetic acid, concentrated sulfuric acid, concentrated nitric acid and the like. However, this polymeric material has only been the starting point for a wide variety of further processes and apparatuses that have attempted to improve the characteristics of the polymer. However, the art filed is in search of processes and/or methods for further improving the characteristics and/or properties of PTFE and/or TFE.
PTFE is generally a white thermoplastic material. As disclosed, depending upon the grade of PTFE, the melting point is generally about 565 degrees Fahrenheit to about 655 degrees Fahrenheit. In its natural state, PTFE has a tendency to agglomerate. Therefore, several methods have been developed in the art field to sinter the PTFE to reduce its agglomeration. Generally, a process that has attempted to reduce the agglomeration characteristics of PTFE has been referred to as attempting to degrade the PTFE (change its crystallinity). However, heretofore, no process has been developed that fully degrades PTFE and/or change the crystallinity as the present invention. In fact, consumers are best to be warned that when purchasing a degraded TFE product from any source, the percent degradation should be verified.
A prior art method of processing and using PTFE has involved the thermal degradation of the PTFE at a temperature in the range of 565 degrees Fahrenheit to 1150 degrees Fahrenheit. While processes of this type have been shown to improve certain characteristics of the PTFE, the partially degraded PTFE still has a tendency to agglomerate. Further, sintering such partially degraded PTFE does reduce the agglomeration, but the sintered product has been extremely hard to commute to a fine particle size less than about five (5) micron particle size, as is illustrated in the article titled xe2x80x9cEffect of PTFE Particle Size on Wear and Coefficient of Frictionxe2x80x9d by Ballester et al., presented at the NLGI 2000 67th Annual Meeting, in paper #0025. Accordingly, the art field is in search of processes for treating PTFE to enable it to improve its characteristics and enable it to be ground to a low micron particle size. In fact, the paper proposes that sintered PTFE can only be ground to average micron sizes of less than five (5) when high doses of irradiation are used. The following table illustrates prior art conception of degradation as it relates to particle size:
As is illustrated, the prior art taught that obtaining a sub micron size degraded PTFE derivative product was best obtained with an unsintered virgin white paste. The art has taught that to obtain submicron particle size for sintered PTFE stock, high doses of irradiation are necessary whereas only low to moderate doses are required for unsintered stock to obtain smaller submicron particle size. There is no teaching that thermal treatment of a PTFE stock material can produce a degraded tetrafluoroethylene product with submicron particle size after grinding.
However, the art field has taught away from further heat treatment degradation (changing crystallinity) of a PTFE derivative and has instead concentrated upon irradiation of PTFE. However, such irradiation has only sterilized the PTFE and not at least partially degraded it. Examples of such irradiation treatment of PTFE may be found in U.S. Pat. No. 3,878,164 (the ""164 patent), U.S. Pat. No. 3,766,031 (the ""031 patent), U.S. Pat. No. 4,029,870 (the ""870 patent), U.S. Pat No. 4,220,511 (the ""511 patent), U.S Pat. No. 4,748,005 (the ""005 patent), U.S. Pat. No. 4,777,192 (the ""192 patent), U.S. Pat. No. 5,891,573 (the ""573 patent), U.S. Pat. No. 5,968,997 (the ""997 patent), U.S. Pat. No. 4,036,718 (the ""718 patent), U.S. Pat. No. 3,766,031 (the ""031 patent), and U.S. Pat. No. 4,052,278 (the ""278 patent). However, none of these patents have produced a degraded derivative tetrafluoroethylene product and thus have not produced an improved degraded derivative tetrafluoroethylene product as is produced by the apparatuses and processes of the present invention.
For example, the ""031 patent states that the heat treating of PTFE should be avoided because of discoloring of the heat treated product. The ""031 patent states that an application of a critical dose of ionizing radiation to the product renders the product capable of comminution to fine particle size. However, the product produced by this process is not at least partially degraded (changed crystallinity) and has not attained an improvement in its lubricant characteristics as the present invention. Accordingly, the art field is in search of a process and apparatus for the heat treating of PTFE for full degradation of the product to obtain a crystallinity whereby the product is not discolored and the lubricant characteristics are improved.
The ""870 patent teaches and discloses an irradiation process for PTFE to obtain a small particle size. The ""870 patent further states that the heat treatment of PTFE is undesirable for producing fine particle size of less than 5 microns. Accordingly, the art field is in search of a method of thermally degrading PTFE and/or changing the crystallinity whereby the product is capable of being ground to a particle size of less than 5 microns and has superior lubricity characteristics.
The ""511 patent teaches and discloses partially degrading PTFE through the use of concurrent or countercurrent heat treatment and irradiation to produce a fine particle size inert product capable of being used as a lubricant in inks. The patent teaches that as the PTFE is degraded the products molecular weight will be reduced. However, the product produced by such method is not as degraded as the present invention nor is the crystallinity altered as in the present invention. As well, the prior art has not produced a PTFE product and/or a PTFE derivative product that can be burnished on a surface. Furthermore, the patent cautions that the PTFE should not be heated much above its melting point during heat treatment. Accordingly, the art field is in search of a method of fully degrading PTFE and/or changing the crystallinity whereby the product is essentially inert with improved lubricant properties.
A further example of how the art field has taught away from the heat treating of PTFE for degradation (changing crystallinity) is disclosed in the ""718 patent. The ""718 patent discloses that the prior art heat treating methods produced a product that was not capable of being milled or ground to a particle size below about 5 microns. The patent states that an irradiation treatment of the PTFE will produce a friable product that is capable of being ground to less than a 5 micron particle size. However, the patent does not produce a product that is at least partially degraded of that has the crystallinity of the present invention. Accordingly, the art field is in search of a process for heat treating PTFE for degradation to alter the crystallinity whereby the product may be milled or ground to a particle size of less than 5 microns and exhibit enhanced lubricity characteristics.
Various other patents describe uses and compositions of PTFE and/or its derivatives. Examples of such patents are U.S. Pat. No. 4,834,894 (the ""894 patent), U.S. Pat. No. 4,888,122 (the ""122 patent), U.S. Pat. No. 5,296,165 (the ""165 patent), and U.S. Pat. No. 5,898,022 (the ""022 patent). The ""894 patent and the ""122 patent teach and disclose the dispersion of PTFE in an oil for an improved reduction in friction. The ""165 patent teaches and discloses the coating of a substance with a PTFE co-polymerized product for improved stainproofing, sliding, and corrosion resistant properties. The ""022 patent teaches and discloses a complex formulation including PTFE for the reduction of friction and repelling of moisture. However, none of these patents teach the use of a degraded derivative tetrafluoroethylene product with changed, enhanced crystallinity, improved lubricity and associated characteristics.
The prior art has recognized the benefits of degrading PTFE to improve the products lubricity characteristics. However, the art field has taught that thermal degradation of the product will not produce a at least partially degraded product that may be ground to a particle size of less than 5 microns that exhibits improved lubricant characteristics. Contrary to the teachings of the art, unexpected results of a degraded derivative tetrafluoroethylene product with changed and/or enhanced crystallinity that can be ground or milled to a particle size of less than 5, may be obtained by the various embodiments of the processes and apparatuses disclosed in this present invention through thermal degradation and/or gas mixing.
The present invention generally relates to processes and apparatuses for the production of a tetrafluoroethylene derivative product with enhanced crystallinity and processes for producing the same. The enhanced crystallinity of the at least partially degraded tetrafluoroethylene derivative product of the present invention imparts unexpected properties of higher heats of fusion than that of ordinary tetrafluoroethylene and/or its derivative products. The new crystalline product has improved lubricity and/or burnishing properties as compared to prior art polymerized tetrafluoroethylene.
This summary is not intended to be a limitation with respect to the features of the invention as claimed and any examples are merely intended as embodiments, and the scope and other objects can be more readily observed and understood in the detailed description of an embodiment and the claims.